Boundaries between hydrophilic and hydrophobic surfaces have previously been utilized in applications where a liquid is to be retained on the hydrophilic side of the boundary for shorter or longer periods of time. In microfluidics this kind of boundary has been used in fluidic functions such as passive valves, anti-wicking functions, vents, liquid-directing functions etc. See for instance: WO 9958245, WO 0185602, WO 02074438, WO 03018198, and WO 03024598 (all of Gyros AB); U.S. Pat. No. 6,926,020, U.S. Pat. No. 6,591,852, U.S. Pat. No. 6,601,613 and U.S. Pat. No. 6,637,463 (all of Biomicro); WO 0190614 (Micronics); WO 9917093 (University of Michigan); U.S. Pat. No. 4,676,274 (Brown); WO 0187486 (Gamera/Tecan); WO 0241996, WO 0242650, and WO 0241995 (all of Pyrosequencing AB); etc.
Hydrophilic surfaces in the form of spots and delineated by boundaries to hydrophobic parts have also been used to collect and/or concentrate aliquots of aqueous liquids to the hydrophilic spots. See for instance U.S. Pat. No. 6,287,872 (Bruker Daltonik GmbH) and WO 9815356 (Molecular Drives Ltd). Hydrophobic spots on a hydrophilic surface have been described in EP 1053784 (Norhoff et al).
A “dispensation” plate comprising on one side larger hydrophilic spots/wells for storing of liquid and on the opposite side smaller hydrophilic spots/wells and a transport capillary between each pair of large and small spot/well. Each hydrophilic spot/well is surrounded by a hydrophobic surface that may be rough. See WO 0107161 (Merck & Co).
Boundaries between hydrophilic and hydrophobic surface areas have been combined with a change in geometric surface characteristics. See the anti-wicking functions described as unit 7 in WO 02074438 (Gyros AB) and the “wells” described in WO 9815356 (Molecular Drives Ltd).
When transporting liquid aliquots through a microchannel structure comprising boundaries of the type discussed above the liquid typically will pass the hydrophobic surface area (surface area 2). Many of the liquids used contain dissolved components that will have a tendency to adsorb to hydrophobic surfaces, for instance surface active components such as detergents and components that exhibit peptide structure (e.g. oligo/polypeptides including proteins). This may be harmful for a fluidic function that is defined by a boundary between a hydrophilic and a hydrophobic surface. The risk for failures in a microchannel structure will increase with its number of surface areas 2/boundaries. The function of valves, vents, anti-wicking functions etc may be disturbed, and not function properly when contacted with liquid a second time, a third etc time etc. Undesired wicking, leakage and spreading of liquid may occur.
Rough/grainy hydrophobic surfaces have been proposed to be particularly suitable for the immobilization of bioaffinity reagents (beads, microtiter wells, fibers tubes etc) (U.S. Pat. No. 5,424,219 (Cytech Biomedical)).